Fix NPE in archetype plugin.

Related to
https://issues.sonatype.org/browse/PR-4758

Problem was multiple:
* no NPE protection, but model might be null after Indexer
  changes (see XXX Igor's comment).
* Archetype plugin never properly "uninstalled" the
  generated item from repo root, only installed
[NEXUS-5782] Use proxy configured for http also for https when https does not have specific configuration
Getting rid of plexus.

After merge (this was in two modules), the module
became "halfling", as plugin was sisu but shared
code was still plexus. Plexus removed,
UTs update too
[NEXUS-5782] Add asserts about proxy being accessed in http/https proxy IT
NEXUS-5784: Added UTs

Two UTs testing the changes:
* NPE does not occur in "inconsistent state"
* event inspector properly installs and uninstalls the catalog item
Removed redundant super() and NPEcheck
NXCM-5396: Realms that have no UserManager pollute logs

This change lessens the log noise, while the information
about "not found user" is still logged.

On instances where some Realm is used that does
not have UserManager implementation (like Kenai Realm is),
the logs would be polluted with a lot of exceptions
on every log-in and UI use (status resource).

A Realm without UserManager is still serving the purpose
well (authc and authz would work just fine), but
operations like "user lookup" all fail due to lack
of UserManager.
Merge pull request #62 from sonatype/nxcm-5396-log-noise

NXCM-5396: Realms that have no UserManager pollute logs
Removed redundant test.
Merge pull request #59 from sonatype/fix-archetype-npe

Fix NPE in archetype plugin.
NXCM-5398: Kenai role was applied unconditionally

Hence, every user, even anonymous got it, even without
logging in into Kenai.

Problem was introduced in commit:
5bec64796705e8f6cc754a4f9d8d5f222959cd12

When the plugin was moved in into OSS sources.
Merge pull request #63 from sonatype/NXCM-5398-kenai-role-applied-unconditionally

NXCM-5398: Kenai role was applied unconditionally
Fix assertions in problem reporting via proxy ITs
Exclude sisu-xmlrpc-client (was used unintended by legacy test suite)
Merge remote-tracking branch 'origin/master' into nexus-is-java7